Recently, considerable research efforts have been devoted to the development of fiber-optic immunosensors. An electromagnetic field generated at a silica-liquid interface by total internal reflection, for example, can be used to excite fluorescence of molecules present at the interface (See U.S. Pat. No. 4,447,546). An antibody immobilized at the surface of a silica optical element can bind its complementary antigen from solution, permitting a fast analysis of antigen concentration in the bulk solution. Silica, which is a promising matrix for high pressure affinity chromatography due to its good mechanical stability, which allows for a rapid purification of proteins, has not been used as a common material in conventional immunodiagnostics and immunopurification. Therefore, less work has been done to better understand antibody immobilization on such a surface than on other surfaces.
Although it is known to immobilize antibodies on a siliceous support or carrier, various disclosures exist in regard to maintaining the antibody in an environment which does not irreversibly denature the antibody, namely, a generally alkaline or neutral pH range (See U.S. Pat. Nos. 3,652,761 and 4,071,409 and Anal. Chem. 1980, 52, 2013-2018). U.S. Pat. No. 3,652,761 for example at Col. 6, lines 57-62 indicates that it is "important" that the pH of the solution be held within a range such that the antibody does not become irreversibly denatured.
Ishikawa et al., in J. of Immunoassay, 1(3), 1980, 385-398 reported that an improved preparation of antibody-coated polystyrene beads for a sandwich enzyme immunoassay could be achieved by exposing the antibody to a low pH environment prior to immobilization. Similarly, Conradie et al., in J. of Immunological Methods, 59, (1983) 289-299 reported a similar effect for the antibody coating of polystyrene plates. The Conradie et al. paper indicates that antibodies or antigens bind tightly to plastic surfaces by simple adsorption as contrasted to the use of "other methods" to covalently bind antigens or antibodies to other solid matrices such as "agarose beads, cellulose, nylon, glass, etc."